1. Field of Invention
The present invention relates generally to web inspection systems and more specifically to smart camera systems for detecting flaws and defects of web material.
2. Background
A xe2x80x9cwebxe2x80x9d is a flat material produced continuously in large quantities and at very high rates. Typical web materiel includes fabrics, sheet metal, paper, and non-woven plastic, etc. Inspection of the web material surface is required during production to find flaws and defects. Failure to detect these flaws and defects may result in thousands of feet of unusable web material. Thus, there exists varying methods of web inspection from manual inspection and sampling to image acquisition, processing and analysis.
FIG. 1 illustrates a traditional system 10 for web inspection utilizing line scan cameras 22 positioned above a web 12. Typically, two types of sensor technology, charge coupled device (CCD) or CMOS, are utilized. While CMOS technology allows the signal processing electronics to be on the same chip as the sensor, CCD sensor technology offers advantages superior imaging quality as compared to CMOS sensors, and stand alone components. Continuing with FIG. 1, high bandwidth camera-specific data cables 34 are required to transfer data from the line scan cameras 22 to a vision processor 32. A typical high bandwidth data stream transfer is forty (40) million pixels per seconds, i.e., 500 Mbits per second for pixels of eight (8) bits.
The megapixel data stream is transferred over the camera-specific cables 34 to frame grabber modules 24 in the vision processor 32. Frame grabber modules 24 utilize standard integrated circuit (IC) boards to digitize an analog video stream image from a line scan camera 22. The digitized images, represented by arrays of numbers, are streamed to pipeline vision processors 26 for real time preprocessing. The pipeline vision processors 26 utilize dedicated image processing boards for data and image analysis that may be different for various webs. For example, a pipeline vision processor 26 may be configured to extract specific information from an image. The processed images from each of the pipeline vision processors 26 are sent to an image analyzer processor 28 that further analyzes and processes an image of the full width of the web 12. The web inspection system 10 of the prior art may further include an image buffer board 30 for data storage. The vision processor 32 of the prior art requires a large chassis to house the IC boards of the frame grabber modules 24, the pipeline vision processors 26 the image analyzer processor, and the image buffer 30.
The processed image from the vision processor 26 is sent to a host computer 14 for display on the graphical user interface (GUI) of the host computer 14. Also connected to the host computer 14, is a defect marker 18 and an encoder 16. The encoder 16 sends information to the host computer 14 including the speed of the web 12. The web 12 typically moves over a rotary device driven by a shaft and roller that produce pulses per unit distance. The host computer 14 utilizes this information to determine the size and position of a defect. The host computer 14 may also include a database input/output board to control a defect marking system 18, and other peripheral device connections 20.
The web inspection systems 10 of the prior art present several disadvantages. As described above, prior art web inspection systems 10 require a high number of components that are supplied by many different manufacturers, thus presenting compatibility problems. Integration of the components is difficult and expensive, and the resulting system is often difficult to configure and use. The prior art web inspection systems 10 typically have large footprints and require racks or large custom boxes of boards for parallel processing. These extra racks of equipment and the operator console, or host computer 14, must be out on the floor and relatively close to the web equipment 12 due to the constraints on the length of connecting cables which must transmit a large bandwidth of data. For example, custom shielded cables are required to connect components to protect the video signal from picking up background noise. The requirement of proprietary cables and the large bandwidth transmission of the high speed raw image data from the cameras limits and/or preempts the use of standard factory ethernet cables to link all components and factory computers.
A further disadvantage of the prior art web inspection systems 10 as shown in FIG. 1 is the low mean time between failure due to the number of components. In addition, a web inspection system 10, as shown in FIG. 1, is an unbalanced architecture, meaning that one component in the system often limits the performance of the system. For example, high speed data sent over cables 34 may jam processing in the vision processing box 32. Also, high defect rates may cause overload occurrences in the image analyzer processor 28. Expansion of an unbalance architecture to add more capability is usually very expensive, and the system 10 is often already maximized, e.g. the rack holding the equipment cannot accept more boards. Another drawback of the non-robust web inspection system 10 of the prior art is that the system 10 is not easily scalable. Therefore, if a customer requires the detection of defects that are half the size that the current system 10 is capable of detecting, more cameras may be added, but the system 10 cannot be configured to accept more pipeline vision processors 26 and/or a second image analyzer 28.
Thus there exists a need for a balanced and robust web inspection system that is easily integrated with an existing manufacturing Ethernet, and is capable of detecting a high rate of web flaws and defects.
It is an advantage of the present invention to provide smart cameras for processing images at the front end of the system to limit the bandwidth required to transmit image data.
It is a further advantage of the present invention to provide a robust web inspection system that is capable of expansion.
It is another advantage of the present invention to provide a web inspection system that may be connected to an existing factory ethernet.
It is yet another advantage of the present invention to provide a web inspection system that can be readily expanded as required.
It is yet another advantage to provide a low contrast web inspection system that is capable of detecting flaws and defects in web material that are close to the noise level.
Still another advantage of the present invention is to provide a web inspection system that requires a limited number of components thus increasing the mean time between failure of the web inspection system.
The present invention also provides a balanced architecture for processing data that results in predictable response and more robust behavior.
In an exemplary embodiment of the present invention, a web inspection system includes at least one smart camera for generating digitized images of portions of a web material having a flaw or defect. Each smart camera is connected via an ethernet hub to a host computer. The host computer and a web encoder monitor the web speed and send control signals to the each smart camera. Each smart camera is connected to a marking system for marking the web proximate to each flaw or defect with corresponding codes or other markings. In an exemplary embodiment each smart camera includes a head board for capturing an image of a portion of a web, and digitizing the image, a processor for analyzing the image, an input/output board for controlling the input and output of the image data signals, and a power supply board for supplying the smart camera components with required voltages.
In an exemplary embodiment of the present invention, the smart camera is capable of detecting very small flaws and defects of the web, i.e. the contrast between a flaw and good web material is close to a noise level. The smart camera of the exemplary embodiment includes all signal processing devices, and only web flaw information and flaw images are sent to the host computer. However, the smart camera is capable of sending any portion of the real-time web image during periods of low bandwidth usage, e.g. when the number of web flaws is minimal.
The smart camera of the exemplary embodiment includes a line scan camera, a lighting uniformity correction and pixel sensitivity correction circuit, a web edge detector circuit, a multi-pipeline flaw detection pre-processor, a run length encoder, a two dimensional blob detector circuit, a two dimensional blob analyzer, and an inspect/reject criteria analyzer. The line scan camera supplies a digital video stream of the web to the lighting uniformity correction and pixel sensitivity correction circuit. Each pixel of the digital video stream is corrected or adjusted according to a pre-determined baseline. The web edge detector determines the location of the edge of the web, and transmits the web edge data and corrected digital video stream to the multi-pipeline flaw detection preprocessor.
The multi-pipeline flaw detection pre-processor of an exemplary embodiment includes programmable two dimensional filters including a background filter, a machine direction streak filter, a cross direction streak filter, and a small flaw filter. Each filter determines an average pixel value along a portion of the web. The average pixel value, which is constantly updated, becomes a reference for an adjacent portion of the web. The multi-pipeline flaw detection pre-processor also includes four adaptive background subtraction channels that subtract the averaged background from the corrected digital video stream, the output of the machine direction streak filter, the output of the cross direction streak filter, and the output of the small flaw filter. In the exemplary embodiment, four multi-group thresholders group pixels for each adaptive background subtraction channel. The four multi-group thresholders include a single pixel flaw detector, a machine direction streak detector, a cross direction streak detector, and a small flaw detector. A fifth multi-group thresholder uniformity detector groups pixels for the output of the background filter. The outputs of the multi-group thresholders are video signals that include potential web flaw data. These signals are sent to a priority logic circuit of the multi-pipeline flaw detection pre-processor to prioritize the signals according to programmable thresholds and rules.
The prioritized signal from the multi-pipeline flaw detection pre-processor is sent to a run line encoder to determine the start and stop pixels for the detected web flaws. A two dimensional blob detector and analyzer perform a connectivity analysis on the continuous stream of prioritized signals to determine whether groups from a same flaw class touch to form blobs, i.e. two dimensional areas of flaw. The resulting output data from the blob analyzer and the prioritized signal is then analyzed by a programmable inspect/reject criteria to determine whether the detected blobs rise to the level of a flaw. The output from the inspect/reject criteria analysis, which includes video and control data, is output from the smart camera to the host computer.
In the exemplary embodiment of the present invention, the host computer records and displays the flaw information, including an image, location information, and the class of the flaw. The host computer may also request real-time video of the web as permitted by the availability of system bandwidth. The host computer of the exemplary embodiment performs trend analysis on the detected web flaws to determine whether any particular web flaw is occurring at a regular interval at a same location on the web. The detection of a regularly occurring flaws may indicate specific problems with the web manufacturing equipment.